Handover-based method for anonymous observation of a moving subscriber

ABSTRACT

A location of a subscriber can be observed by means of a mobile network in a completely anonymous way, without a subscriber identifier or a temporary subscriber identifier. At first, a method extracts from a first time slot of a radio channel a message which includes information about a second time slot of a radio channel. The first time slot of a radio channel discloses the current cell of the subscriber and the second time slot of a radio channel discloses a new cell of the subscriber. A location of the subscriber is determined on the basis of the current and the new cell. This location is approximately situated in a geographical intersection area of the current and the new cell. Different kinds of statistics can be deduced from the observations concerning activities of subscribers.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of PCT Application No. PCT/FI2004/050031, filedon Mar. 22, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to collecting information aboutmoving subscribers by means of a mobile network.

2. Description of the Related Art

In general, it is known to use a mobile network for locatingsubscribers, but the mobile network can be used in new ways forlocalization. For example, the applicant's prior patent applicationsFI20012139 and FI20030086 describe new ways to utilize mobile networks.These two patent applications and the present application share thecharacteristic in which way certain basic features of the mobilenetworks are utilized for locating mobile subscribers.

Patent application FI20030086 discloses such basic terms of prior artthat are relevant also for the invention of the present application,thus we refer to the said patent application as an information sourcefor the basic terms.

The method described in patent application FI20030086 comprises thefollowing steps. At first, messages belonging to a certain message setare collected from the areas of a mobile network in which a terminalcommunicates with the mobile network using messages of the message set.These areas are border areas that are situated between location areas ofthe mobile network. Depending on a statistical survey, or anotheranalysis to be performed, the border areas may be, for example, suchroad stages on which velocities of vehicles are measured. In general,the border areas are areas through which mobile subscribers move to theareas interested in a survey, or from which users can move out. Thenumber of different types of users can be calculated by detecting theusers' movements in the border areas. If required, the velocities of theusers can also be calculated. When a message includes a temporarysubscriber identifier, it is used for fetching a subscriber identifierfrom a subscriber database or from the subscriber data stored in amemory. Lastly, initial data is formed using subscriber identifiers. Apart of those subscriber identifiers may be from the collected messagesand another part may be from the subscriber data. A single subscriberidentifier may be, for example, an IMSI that includes the followinginformation: an initial value disclosing a country, an initial valuedisclosing an operator, and an initial value disclosing a subscriber.

FIG. 1 shows ways to implement the system described in the patentapplication FI20030086, assuming that the system is constructed within amobile communication system. In the first embodiment network elements,such as signal analyzers 151, are added to the mobile communicationsystem. Traffic important for the invention, i.e. the traffic betweenbase stations and base station controllers, is monitored by means of theadded network elements. The signal analyzer 151 is preferably connectedto the point P1 in order to monitor signal traffic which is led througha 2 Mb E1 cable from a base station to a base station controller. Morethan one signal line can be assigned to the same base stationcontroller, for example, the point P2 in FIG. 1. Typically one signalanalyzer monitors from eight to sixteen E1 connections, each of whichcan be connected to twelve transmitter/receiver units, i.e. TRXs, whenusing the GSM technique. The signal analyzer 151 may include a userinterface for specifying necessary information and the messages to bemonitored. When the signal analyzer 151 detects a message of a certaintype on the basis of an identifier of the message, the signal analyzercollects said message and sends data in accordance with its definitionsto the address of the predetermined calculating server 150. The addressof said server may be, for example, an IP or another network address,and/or a port address. If the system is intended for calculatingvelocities of subscribers, the velocities can be stored in the trafficdatabase 155.

Network elements, such as the signal analyzer 152, are used in thesecond embodiment of the system. They are connected to monitor at thelocation points P3 traffic between a base station controller and theexchange 103 or the VLR 102.

Network elements, such as base stations, base station controllers,exchanges, or a VLR, are changed in the third embodiment. These elementscan send certain messages to the server in order to collect informationneeded for the localization process.

In the fourth embodiment known charging records, such as the CDR(Charging Data Record), are used in a new way. In this embodiment anexchange of a mobile network, e.g. an MSC, is adapted to write acharging record when a terminal is moved into and out of a certainlocation area. For example, when the terminal 101 detects that the LAIof a new cell differs from the LAI of the cell that had the bestaudibility a little while ago, the terminal informs the VLR 102 via theMSC 103. Then the MSC receives a Location Updating Request message sentby the terminal, writes a charging record, and sends the chargingrecord, or at least a part of its data content 160 either directly orvia a data storage unit to the calculating server 150. Depending on theequipment deliverer, the data content 160 may include identifier data,such as an IMSI. Because it is possible to listen to the radiointerface, hostile parties may locate users of the mobile networkwithout their knowledge. In order to avoid this, a pseudo identifier,i.e. Temporary Mobile Subscriber Identity (TMSI), is taken into use. Therelation between the TMSI and IMSI is stored in the VLR and in themobile phone.

The above-described embodiments are related to the following drawbacks.

First, borders of location areas are not necessarily situated in theareas where movements of subscribers interested in a statistical surveyare happening. This especially concerns the location area defined by aLocation Area Identifier (LAI) or a Location Area Code (LAC) identifier(a LAI includes a LAC together with a country identifier or an operatoridentifier). In the method of the patent application FI20030086observations about users are usually obtained, for example, when alocation area (LAC) of a subscriber and a TMSI of the subscriber change.

Secondly, use of TMSI identifiers for locating subscribers cause VLRrequests which load the mobile network.

Thirdly, the successful use of the TMSI identifiers requires that, ifneeded, the IMSI identifiers related to the TMSI identifiers can befetched from a network of another mobile operator. It is possible thatthe other mobile operator is not co-operative in this matter, or thefetching of the IMSI identifiers becomes too expensive.

Fourthly, even use of TMSIs for the localization may be problematicbecause of data privacy and data security.

SUMMARY OF THE INVENTION

One of the objectives of the invention is to eliminate the drawbacks ofa location system which utilizes a mobile network. A subscriber can belocated in a completely anonymous way, without a subscriber identifieror a temporary subscriber identifier. In addition, the areas that are tobe located in a statistical survey, or in another analysis, can beselected from a larger set of areas. Instead of LAC areas, it ispossible to select cells inside the LAC areas.

The basic idea of the inventive method is to extract messages that areincluded in handover commands. A HandOver Command message sent by amobile network is, for example, such a message. Observations concerningsubscribers of the mobile network are based on the extracted messages.For example, the location information of a subscriber or the velocity ofthe subscriber may be observed in a certain point of time. Differenttypes of statistics that describe an activity of subscribers can becalculated on the basis of these observations.

The method for locating a subscriber comprises the following steps. Amessage, which includes a piece of information about a second time slotof a radio channel, is extracted from a first time slot of a radiochannel. The first time slot of a radio channel determines the currentcell/location of the subscriber and the second time slot of a radiochannel determines a new cell/location of the subscriber. Thus, thesecond time slot of a radio channel is taken into use during thehandover of the subscriber of the mobile network. Then the location ofthe subscriber is determined on the basis of the current cell and thenew cell, i.e. the location of the mobile station is at least partlylocated in the geographical intersection of the current cell and the newcell.

The method further comprises the following steps for calculating thevelocity of the subscriber. At first, the method attaches a time stampto the message disclosing the location. The method also stores themessage and its time stamp in a memory, wherein the time stamp disclosesa point of time when the message was extracted. When the current cell ofthe subscriber is changed to a new cell and the subscriber is movingfrom the new cell to a subsequent cell, the method extracts the messagetransmitted in the mobile network in a second time slot of a radiochannel. The said message includes information about a third time slotof a radio channel, which has been started to be used during thesubsequent handover of the subscriber of the mobile network. The thirdtime slot defines the subsequent cell of the subscriber. The methoddetermines another location of the subscriber on the basis of the newcell and the subsequent cell. The other location is at least partlysituated in the intersection of said cells. The method determines adistance travelled by the subscriber on the basis of the second locationand the location stored in the memory. The method determines thevelocity of the subscriber on the basis of the distance travelled by thesubscriber and the time stamp disclosing the point of time of the firstextracted message, and on the basis of the time stamp disclosing thepoint of time of the second extracted message.

A system according to the invention utilizes the above-described method.The system preferably comprises signal analyzers for extractingmessages. By examining said messages a subscriber can be quite assuredlyobserved in the area of interest in a statistic survey or in anotheranalysis.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described more closely with reference to theaccompanying drawings, in which

FIG. 1 shows operation of a prior art location system;

FIG. 2 shows an example of locating a subscriber by means of the messagecontaining a handover command;

FIG. 3 shows an example of measuring a subscriber's velocity by means ofthe message containing a handover command; and

FIG. 4 shows operation of the system for locating subscribers.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Maybe the most unique characteristic of the invention is that asubscriber/mobile station is located on the basis of just one message.In this regard the present invention differs from the method describedin patent application FI20030427 in which a subscriber/mobile station islocated by means of a message pair.

FIG. 2 shows an example of locating a subscriber by means of the messagecontaining a handover command. Said message (as messages in general) isreceived in a certain time slot of a radio channel. Radio channels areallocated to base stations of the mobile network. Each radio channel istypically divided into eight time slots so that usually one time slot isin use by one subscriber. When said message containing the handovercommand is received from a certain time slot of a radio channel, it canbe determined that the time slot defines a cell in which the subscriberis currently located. When the received message normally includes a new(location) cell of the subscriber, two pieces of cell information areusable in the method. The method determines that the subscriber issituated in the geographical intersection of the current cell and thesubsequent cell of the subscriber. Let us assume that 1) the messagecontaining a handover command is a HandOver Command message, 2) “cell B”is the cell of interest, 3) signalling of the time slots 201 allocatedto cell B are observed by a signal analyser. Let us further assume that4) signalling of time slots 202 allocated to cell B's “neighbor cell A”are observed by the signal analyser and 5) signalling of time slots 203allocated to cell B's “neighbor cell C” are observed by the signalanalyser. At first, a time slot of a radio channel 204 allocated to cellA is in use by the subscriber ‘X’. When the HandOver Command message isreceived from the channel, a time slot of a radio channel 205 allocated,for example, to cell B, is read from the message. Then subscriber ‘X’ islocated in the intersection area of cell A and cell B and subscriber ‘X’is arriving to cell B. For this reason, the time slot of a radio channel205 is observed. When subscriber ‘X’ sooner or later leaves the area ofcell B, the HandOver Command message is received from the time slot of aradio channel 205. Then the time slot of a radio channel 206 allocated,for example, to cell C, is read from the said message. At that timesubscriber ‘X’ is located in the intersection area of cell B and cell Cand he/she is leaving cell B.

The present invention is partly based on the method described in patentapplication FI20030086. A temporary subscriber identity is used in thisprior method. Because the temporary subscriber identity usually changesat the borders of LACs, the location areas known by the prior method arein practice LACs. The areas observed in the present invention are cells.

In the prior method the message traffic is observed in the border areasof two LACs. In the first embodiment of patent application FI20030427the message traffic is observed in the border areas of two cells. Thepresent invention differs from the prior method and this firstembodiment, because the distance travelled by a subscriber stretchesthrough the whole cell and said distance is used for calculating thevelocity of the subscriber.

FIG. 3 shows an example of locating a subscriber according to the secondembodiment of the invention. In the second embodiment locating is basedon a message pair so that the messages are obtained during twohandovers. The figure shows three cells 301, 302, and 303, thegeographical intersection area 304 between the cells 301 and 302, andthe geographical intersection area 305 between the cells 302 and 303. Avehicle 307 can be also seen in the figure travelling from the cell 301along a road 306 toward the cell 302, the vehicle carrying a mobilestation with it. A first message is received from intersection area 304of the cells and a second message is received, when the vehicle movesahead to intersection area 305. In more detail, when the messages areHandOver Command messages, the first message is obtained from the borderarea 308 of intersection area 304 and the second message is obtainedfrom the border area 309 of intersection area 305. The velocity of thevehicle is measured so that the distance travelled by the vehicle is thedistance from border area 308 along the road 306 to border area 309 andthe time lapsed during the travel is the time interval from the point oftime when the first message was received to the point of time when thesecond message was received.

The messages used in locating are preferably messages that aretransmitted or received by a mobile network and that are extractedthrough the Abis interface from the signalling traffic. In that case theabove-mentioned “a time slot of a radio channel” is a signalling timeslot of an E1 link of the Abis interface. It is reasonably simple toimplement monitoring of the messages of a base station controller, or inmore general, monitoring of the messages of a mobile network. Themessages to be extracted may also be messages that are transmitted inair interface.

FIG. 4 shows the operation of the method for locating subscribers. Themethod comprises the step of extracting from a first time slot of aradio channel a message which includes a piece of information about asecond time slot of a radio channel. The first time slot of a radiochannel determines the current cell of a subscriber. The second timeslot of a radio channel is taken into use during a handover of thesubscriber, i.e. the second time slot of a radio channel determines anew cell of the subscriber. The method also comprises the step ofdetermining a location of the subscriber on the basis of the current andthe new cell. Said location is at least partly situated in thegeographical intersection of the current and the new cell.

In addition to the location of the subscriber, the steps shown in FIG. 4also result in information about the direction in which the subscriberis moving. These pieces of information are often adequate from the pointof view of a statistical survey, or another analysis. When needed, thevelocity of the subscriber can also be calculated. The velocity isobtained by using the way shown in FIG. 3. The distance travelled by thesubscriber is the distance between the border areas 308 and 309 and thetime lapsed for the travel is the time interval between the messagesobtained from these border areas. As shown in the above FIG. 2,subscriber ‘X’ can be traced from one cell to another, if needed. Ademand for this kind of tracing depends on the analysis to be performed.

The locating system according to the invention is at least adapted toperform the method steps shown in FIG. 4. As shown in FIG. 1, one ormore signal analysers can be utilized in the system. However, it isobvious for a person skilled in the art that a system according to theinvention can also be implemented in other ways.

Thus, while there have shown and described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements and/ormethod steps shown and/or described in connection with any disclosedform or embodiment of the invention may be incorporated in any otherdisclosed or described or suggested form or embodiment as a generalmatter of design choice. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

1. A method for locating anonymously subscribers, said subscribersmoving between cells of a mobile network, characterized by the steps ofextracting by extracting means a first message transmitted in the mobilenetwork, the first message defining a current cell of a subscriber ofthe mobile network and the first message including a piece ofinformation on the basis of which a second message transmitted in themobile network is to be extracted, extracting by the extracting meansthe second message which defines a new cell of the subscriber, whereinthe first message and the second message are sent from a base stationand/or a base station controller of the mobile network due to at leastone handover performed for the subscriber, and determining by acalculating server a location of said subscriber on the basis of thecurrent cell defined by the first message and the new cell defined bythe second message, wherein the location is at least partly situated ina geographical intersection of the cells defined by the first and thesecond message.
 2. The method as in claim 1, characterized in that thefirst message is a HandOver Command message and the second message isone of the following messages: a Channel Activation, a ChannelActivation Acknowledgement, or a HandOver Detect message.
 3. The methodas in claim 1, characterized in that the piece of information is a timeslot of a radio channel.
 4. The method as in claim 2, characterized inthat the piece of information is a reference number of a handover whenthe second message is a Channel Activation message.
 5. The method as inclaim 2, characterized in that a first time stamp is attached to thefirst message which discloses a point of time when the first message wasextracted, a second time stamp is attached to the second message whichdiscloses a point of time when the second message was extracted, and onthe basis of a location read from a memory and another location, adistance which the subscriber has travelled is determined and a velocityof the subscriber is determined on the basis of the distance of, thefirst time stamp, and the second time stamp, wherein the distancetravelled by the subscriber is the distance between two border areassituated in the geographical intersection of the cells defined by thefirst and the second message.
 6. The method as in claim 1, characterizedin that the second message is a HandOver Command message and the firstmessage is one of the following messages: a Channel Activation, aChannel Activation Acknowledgement, or a HandOver Detect message.
 7. Themethod a sin claim 6, characterized in that a time stamp is attached tothe location disclosing a point of time when the second message wasextracted and the location of the subscriber, which was firstdetermined, is stored in a memory, and when the current cell of thesubscriber is changed to the new cell and the subscriber is moving fromthe new cell to a subsequent cell, a third message transmitted in themobile network is extracted, the third message disclosing the subsequentcell of the subscriber, another location of the subscriber is determinedon the basis of the new cell defined by the second message and thesubsequent cell defined by the third message, the location stored in thememory is read, and on the basis of the read location and the otherlocation, the distance that the subscriber has travelled across the newcell is determined and a velocity of the subscriber is determined on thebasis of the distance travelled by the subscriber, the time stampdisclosing the point of time when the second message was extracted, andon the basis of another time stamp disclosing the point of time when thethird message was extracted.
 8. The method as in claim 1, characterizedin that the extracting means comprises at least one signal analyzerwhich is adapted to send data the calculation server.
 9. The method asin claim 1, characterized in that a signal first message and the secondmessage are extracted from signal traffic of at least one E1 connection.10. A system for locating anonymously subscribers, said subscribersmoving between cells of a mobile network, characterized in that thesystem is adapted to: extract by extracting means a first messagetransmitted in the mobile network, the first message defining a currentcell of a subscriber of the mobile network and the first messageincluding a piece of information on the basis of which a second messagetransmitted in the mobile network is to be extracted, the extractingmeans comprising at least one signal analyzer adapted to send data to acalculation server, extract by the extracting means the second messagewhich defines a new cell of the subscriber, wherein the first messageand the second message are sent from a base station and/or a basestation controller of the mobile network due to at least one handoverperformed for the subscriber, and determine by the calculating server alocation of the subscriber on the basis of the current cell defined bythe first message and the new cell defined by the second message,wherein the location is at least partly situated in a geographicalintersection of the cells defined by the first and the second message.11. The system as in claim 10, characterized in that the first messageis a HandOver Command message and the second message is one of thefollowing messages: a Channel Activation, a Channel ActivationAcknowledgement, or a HandOver Detect message.
 12. The system as inclaim 10, characterized in that the piece of information is a time slotof a radio channel.
 13. The system as in 11, characterized in that thepiece of information is a reference number of a handover when the secondmessage is a Channel Activation message.
 14. The system as in claim 11,characterized in that the system is adapted to: attach to the firstmessage a first time stamp which discloses a point of time when thefirst message was extracted, attach to the second message a second timestamp which discloses a point of time when the second message wasextracted, and on the basis of a location read from a memory and anotherlocation, determine a distance which the subscriber has travelled, anddetermine a velocity of the subscriber on the basis of the distance, thefirst time stamp, and the second time stamp, wherein the distancetravelled by the subscriber is a distance between two border areassituated in the geographical intersection of the cells defined by thefirst and the second message.
 15. The system as in claim 10,characterized in that the second message is a HandOver Command messageand the first message is one the following messages: a ChannelActivation, a Channel Activation Acknowledgement, or a HandOver Detectmessage.
 16. The system as in claim 15, characterized in that the systemis adapted to: attach to the location of the subscriber a time stampdisclosing a point of time when the second message was extracted, storethe location, which was first determined, in a memory, and in order toprepare for a situation when the subscriber moves from the new cell to asubsequent cell extract a third message which discloses the subsequentcell of the subscriber, determine another location of the subscriber onthe basis of the new cell defined by the second message and thesubsequent cell defined by the third message, read the location storedin the memory, determine a distance which the subscriber has travelledacross the new cell, the determination of the distance being based onthe read location and said other location, and determine a velocity ofthe subscriber on the basis of the distance travelled by the subscriber,the time stamp disclosing the point of time when the second message wasextracted, and another time stamp disclosing the point of time when thethird message was extracted.
 17. The system as in claim 10,characterized in that the first message and the second message areextracted from signal traffic of at least one E1 connection.
 18. Thesystem as in claim 10, characterized in that the first message and thesecond message are extracted through Abis interface.